The plasma membrane from Dictyostelium discoideum was routinely purified 30-35 fold by an improved techniques using beads coated with positively charged polymers. Cells were attached to the beads and bare regions between the cells were neutralized with polyanions. The neutralization decreased contamination of the bare regions by intracellular proteins released when cells were disrupted to leave behind beads coated by plasma membrane. The neutralization increased the purification as measured by membrane bound 125I-Conconavalin A. Contamination by markers for various intracellular components was markedly decreased. Various bare site neutralization reagents were evaluated and gave different results depending upon their charge density and molecular weight. The pH of the neutralization was critical. The optimum pH for cell attachment to beads, 5.0, had little effect at bare site neutralization. A procedure was devised so that measurements of direct binding of proteins to the exposed cytoplasmic surface can be done. Actin was dissociated from plasma membrane isolated by the improved procedure. It could be reassociated and the amount bound depended upon the actin concentration. KCl at concentrations conducive to filament formation increased binding. Trypsinization of the isolated membranes abolished binding. Chymotrypsin had no effect on binding. Cells grown to late log but prior to stationary phase were used since the actin isolated with the plasma membranes from the latter could not be completely removed.